Extended altitude combustion system

ABSTRACT

A combustion system for performing stable combustion and flame stabilization at high altitudes is described. A primary liquid hydrocarbon fuel is atomized and vaporized within the main combustor chamber to produce a primary fuel vapor. When the combustion system operates at a high altitude, a secondary gaseous fuel is fed into the inlet air port such that the secondary fuel mixes with air, thereby enabling the mixture of the air and the secondary fuel to combust in a catalytic reactor to produce high temperature, oxygen-rich gases that flow into the main combustor chamber. Proper proportional amounts of the two fuels are determined as a function of altitude.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air-breathing gas turbine combustor.More particularly, the present invention relates to an air-breathing gasturbine combustor that enables stable combustion over a range ofaltitudes from sea level to at least 100,000 feet above sea level.

2. Related Art

The present invention provides a novel air breathing gas turbinecombustor concept enabling stable combustion over a range of altitudesfrom sea level to at least 100,000 feet above sea level through the useof two fuel types and catalytic reactor technology. It is well knownthat conventional gas turbine combustors fueled by liquid hydrocarbonsare well characterized and provide high performance and broad flamestability limits at altitudes from sea level up to about 60,000-70,000feet above sea level. An illustration of an exemplary conventional gasturbine combustor 100 is shown in FIG. 1. A conventional gas turbinecombustor design such as that shown in FIG. 1 generally provides highperformance and broad flame stability at low altitudes.

However, above these altitudes, for conventional combustors such as thatshown in FIG. 1, the combustor operating pressure and air inlettemperature typically drop enough to slow vaporization rates andreaction kinetics such that conventional flame holding techniques areineffective. This, in turn, causes significant difficulties with respectto flame stabilization. Thus, the present inventors have recognized theneed for an improved technique for performing combustion at highaltitudes while maintaining flame stability.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a combustion system for performingstable combustion and flame stabilization at high altitudes. The systemcomprises: a first source for providing a primary liquid hydrocarbonfuel; a second source for providing a secondary gaseous fuel; an inletair port; a catalytic reactor coupled to the inlet port; a maincombustor chamber coupled to the catalytic reactor; and an outlet portcoupled to the main combustor chamber. The first source is configured toprovide the primary fuel directly into the main combustor chamber suchthat the primary fuel is atomized and vaporized within the maincombustor chamber to produce a primary fuel vapor. When the combustionsystem operates at an altitude higher than a first predeterminedaltitude threshold, the combustion system is configured to use thesecond source to provide the secondary fuel into the inlet air port suchthat the secondary fuel mixes with air entering the inlet air port, andto cause the mixture of the air and the secondary fuel to combust in thecatalytic reactor to produce a gaseous secondary fuel product that flowsinto the main combustor chamber, such that the main combustor chambercontains a first proportional amount of the primary fuel vapor and asecond proportional amount of the gaseous secondary fuel product.

The first predetermined threshold altitude may be greater than or equalto 60,000 feet above sea level. As the altitude at which the combustionsystem increases from 60,000 feet above sea level to a secondpredetermined altitude threshold, the first proportional amount maydecrease and the second proportional amount may increase. The secondpredetermined altitude threshold may be greater than or equal to 95,000feet above sea level.

When the combustion system operates at an altitude higher than thesecond predetermined altitude threshold, the system may be configured tooperate by using the secondary fuel exclusively at altitudes less thanor equal to a third predetermined altitude. The third predeterminedaltitude may be greater than or equal to 110,000 feet above sea level.

The secondary fuel may be produced by decomposition of a monopropellant.The monopropellant may comprise hydrazine. Alternatively, the secondaryfuel may be produced by gasification of a pure fuel. The pure fuel maybe selected from the group consisting of hydrogen, methane, and propane.

In another aspect, the present invention provides a combustion systemfor performing stable combustion and flame stabilization at highaltitudes. The system comprises: a first source for providing a primaryliquid hydrocarbon fuel; a second source for providing a secondarygaseous fuel; an inlet air port; a catalytic reactor coupled to theinlet port; a main combustor chamber coupled to the catalytic reactor;and an outlet port coupled to the main combustor chamber. When thecombustion system operates at an altitude lower than a firstpredetermined altitude threshold, the combustion system is configured touse the first source only to provide the primary fuel directly into themain combustor chamber such that the primary fuel is atomized andvaporized within the main combustor chamber to produce a primary fuelvapor. When the combustion system operates at an altitude higher thanthe first predetermined altitude threshold, the combustion system isconfigured to use the second source only to provide the secondary fuelinto the inlet air port such that the secondary fuel mixes with airentering the inlet air port, and to cause the mixture of the air and thesecondary fuel to combust in the catalytic reactor to produce a gaseoussecondary fuel product that flows into the main combustor chamber.

In yet another aspect of the invention, a method for performing stablecombustion and flame stabilization at high altitudes is provided. Themethod comprises the steps of: providing a primary liquid hydrocarbonfuel to a main combustor chamber; atomizing and vaporizing the primaryfuel to produce a primary fuel vapor within the main combustor chamber;when an altitude at which the combustion is performed exceeds a firstpredetermined threshold altitude, providing a secondary gaseous fuel toan inlet air port such that the secondary fuel mixes with air in theinlet air port; and combusting the mixture of air and secondary fuel ina catalytic reactor to produce a gaseous secondary fuel product thatflows into the main combustor chamber, such that the main combustorchamber contains a first proportional amount of the primary fuel vaporand a second proportional amount of the secondary fuel vapor.

The first predetermined threshold altitude may be greater than or equalto 60,000 feet above sea level. The step of combusting the mixture ofair and secondary fuel in a catalytic reactor may further comprisecombusting the mixture of air and secondary fuel in a catalytic reactorto produce a gaseous secondary fuel product that flows into the maincombustor chamber, such that the main combustor chamber contains a firstproportional amount of the primary fuel vapor and a second proportionalamount of the gaseous secondary fuel product and such that as thealtitude at which the combustion system increases from 60,000 feet abovesea level to a second predetermined altitude threshold, the firstproportional amount decreases and the second proportional amountincreases. The second predetermined altitude threshold may be greaterthan or equal to 95,000 feet above sea level.

When the combustion system operates at an altitude higher than thesecond predetermined altitude threshold, the method may further comprisethe step of using the secondary fuel exclusively at altitudes less thanor equal to a third predetermined altitude. The third predeterminedaltitude may be greater than or equal to 110,000 feet above sea level.

The secondary fuel may be produced by decomposition of a monopropellant.The monopropellant may comprise hydrazine. Alternatively, the secondaryfuel may be produced by gasification of a pure fuel selected from thegroup consisting of hydrogen, methane, and propane.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features and advantages of the present invention will best beunderstood by reference to the detailed description of the preferredembodiments that follows, when read in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a conventional gas turbine combustor.

FIG. 2 illustrates a dual fuel gas turbine combustor for performingcombustion at high altitudes while maintaining flame stability accordingto a first preferred embodiment of the present invention.

FIG. 3 illustrates a dual fuel gas turbine combustor for performingcombustion at high altitudes while maintaining flame stability accordingto a second preferred embodiment of the present invention.

FIG. 4 illustrates a dual fuel gas turbine combustor for performingcombustion at high altitudes while maintaining flame stability accordingto a third preferred embodiment of the present invention.

FIG. 5 illustrates a dual fuel gas turbine combustor for performingcombustion at high altitudes while maintaining flame stability accordingto a fourth preferred embodiment of the present invention.

FIG. 6 shows a flow chart for a method of performing high-altitudecombustion while maintaining flame stability according to a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In order to address the aforementioned shortcomings of conventional gasturbine combustors for high-altitude operation, the present inventorshave developed a high-altitude gas turbine engine. As used inconjunction with a preferred embodiment of the present invention, ahigh-altitude gas turbine engine is referred to as the HydrazineDecomposition Air Turbine (HDAT). Referring also to U.S. patentapplication Ser. No. 12/323,820, filed Nov. 26, 2008, the contents ofwhich are incorporated herein in their entirety, the HDAT utilizes acatalytic combustor to facilitate stable combustion of hydrazinedecomposition products, composed of gaseous hydrogen and nitrogen at atemperature of 400° F. or higher, with air at high altitudes.Preliminary combustor testing has proved the feasibility of thiscombustor concept at fuel lean mixture ratios and pressure levelscommensurate with altitudes of approximately 95,000 feet above sealevel. Further, the present inventors believe that stable combustionusing the HDAT system may be achieved at altitudes of up to 110,000 feetabove sea level. The HDAT system is also capable of operating ataltitudes lower than 65,000 feet above sea level. However, the overallfuel consumption of the HDAT is generally inferior to that of gasturbines fueled by conventional liquid hydrocarbons, which provide goodperformance at such low altitudes.

Referring generally to FIGS. 2, 3, 4, and 5, in accordance with apreferred embodiment of the present invention, the Extended AltitudeCombustion System (EACS) described herein enables a dual fuel gasturbine for which a primary fuel, typically a conventional liquidhydrocarbon such as aviation grade kerosene, serves as the sole fuelsource at low altitudes (i.e., under approximately 65,000 feet above sealevel). As altitude is increased to a point at which liquid hydrocarbonflame stability begins to deteriorate, a secondary gaseous fuel issupplied to the system. In one preferred embodiment of the invention,the secondary fuel is produced through the decomposition of anappropriate monopropellant, such as hydrazine, or any chemical that hassufficient decomposition energy and suffice heat of combustion with air.In another preferred embodiment of the invention, the secondary fuel isproduced through gasification of a pure fuel, such as hydrogen, methane,or propane, or any other gasified pure fuel that has been shown to havehigh reactivity in the presence of a catalyst at low pressures. Thegasification process may be enabled, for example, by a heat exchangersystem, or by a throttle valve.

Referring to FIG. 2, in one exemplary embodiment of a system 200according to a preferred embodiment of the invention, the secondarygaseous fuel mixes with the compressor air in an inlet air port 12 at afuel-lean mixture ratio before entering a catalytic reactor 22 ofappropriate length, porosity, and material makeup (i.e., washcoat andsupport). The mixture combusts within the catalytic reactor 22. Theresulting high-temperature, oxygen-rich combustion products then enterthe main combustor chamber 14, which is otherwise similar to aconventional gas turbine combustor such as that shown in FIG. 1. Withinthe main combustor chamber 14, the aforementioned combustion productsatomize and vaporize the injected liquid fuel (i.e., the primary fuel),mix with the resulting fuel vapor, and react further. This processfacilitates increased kinetic rates and consequently broadens thestability limits of the liquid-fueled combustor system 200. As a result,the system 200 is able to maintain the low specific fuel consumptionlevels commensurate with liquid hydrocarbons at altitudes higher thanapproximately 65,000 feet above sea level, where operation with thesefuels would otherwise be difficult. The system 200 also includes anoutlet combustor exhaust duct 16.

As altitude increases further, the system 200 becomes more and morereliant on the secondary fuel flow for combustion stability untileventually a point is reached where combustor pressure has dropped lowenough that the primary fuel flow is totally ineffective. At this point,in a preferred embodiment of the present invention, the combustor system200 is capable of operating solely on the secondary fuel flow and thecatalytic reactor 22. In one advantageous application of the presentinvention, the combustor system 200 provides aircraft with thecapability of taking off from the ground and climbing to altitudes of upto 110,000 feet above sea level.

The main combustor chamber 14 may be formed or shaped in a variety ofpossible modes, depending on operational and geometric constraints. Forexample, the main combustor chamber 14 illustrated in FIGS. 1 and 2 usesa conventional, through-flow, rich burn-quick quench mix-lean burn (RQL)combustor configuration. However, other widely used variations, such asa lean premixed prevaporized (LPP) combustor or a reverse flowcombustor, may also be incorporated into the system according to apreferred embodiment of the invention.

In another preferred embodiment of the present invention, the combustorsystem may be configured to transition abruptly from the exclusive useof a primary fuel comprising a liquid hydrocarbon fuel to the exclusiveuse of a secondary gaseous fuel. This alternative configuration offersflexibility with respect to catalytic reactor placement, although mostcommonly used catalyst materials are susceptible to poisoning by heavyhydrocarbon fuel vapor and thermal degradation when exposed to hightemperatures. For example, referring to FIG. 3, in a system 300according to another preferred embodiment of the present invention, thecatalytic reactor 22 may be positioned within the dilution air passage.Alternatively, referring to FIG. 4, in another system 400 according toan exemplary preferred embodiment of the present invention, thecatalytic reactor 22 may be positioned downstream of the dilution zone,in the combustor exhaust duct. Referring to FIG. 5, in anotheralternative system configuration 500 according to yet another preferredembodiment of the present invention, the catalytic reactor 22 may beused in a multiple stage configuration. Typically, the position andconfiguration of the catalytic reactor 22 will be selected based on avariety of considerations, such as the required size of the catalyst,the thermal tolerances of the catalyst, and system compatibilityrequirements. The multiple stage configuration of FIG. 5 may be used,for example, in expendable systems with short operational lifetimes,such as gas turbine powered missiles, for which some catalystdegradation may be acceptable.

The method of transition between the primary fuel and the secondary fuelis generally intended to avoid thermal damage to combustor componentsand also to avoid loss of thrust. In configurations for which thecatalytic reactor is positioned downstream of the fuel injection point,such as those illustrated in FIGS. 3, 4, and 5, electromechanicallyactuated flow diversion devices may be used advantageously to ensure astable transition.

The altitude at which operation is abruptly transitioned from theprimary liquid hydrocarbon fuel to the secondary gaseous fuel isdependent upon the stability limits of the hydrocarbon fuel. Typically,this altitude will be within the range of approximately 50,000 feetabove sea level to approximately 70,000 feat above sea level. Theselection of the transition altitude is made so as to maximize systemperformance and utility.

Referring to FIG. 6, a flowchart 600 illustrates a method for performinghigh-altitude combustion while maintaining flame stability according toa preferred embodiment of the present invention. In the first step 605,a primary liquid hydrocarbon fuel is provided to a main combustorchamber. In the second step 610, the primary fuel is atomized andvaporized to produce a primary fuel vapor within the main combustorchamber.

In the third step 615, when an altitude at which the combustion isperformed exceeds a first predetermined threshold altitude, a secondarygaseous fuel is provided to an inlet air port such that the secondaryfuel mixes with air in the inlet air port. In the fourth step 620, themixture of air and secondary fuel is combusted in a catalytic reactor toproduce a high-temperature, oxygen-rich gaseous secondary fuel productthat flows into the main combustor chamber. In the fifth and final step625, appropriate proportional amounts of the primary fuel vapor and thehigh-temperature, oxygen-rich gaseous secondary fuel product aredetermined based on altitude, and the proper proportional amounts arethereby provided.

While the foregoing detailed description has described particularpreferred embodiments of this invention, it is to be understood that theabove description is illustrative only and not limiting of the disclosedinvention. While preferred embodiments of the present invention havebeen shown and described herein, it will be obvious to those skilled inthe art that such embodiments are provided by way of example only.Numerous variations, changes, and substitutions will now occur to thoseskilled in the art without departing from the invention.

1. A combustion system for performing stable combustion and flamestabilization at high altitudes, comprising: a first source forproviding a primary liquid hydrocarbon fuel; a second source forproviding a secondary gaseous fuel; an inlet air port; a catalyticreactor coupled to the inlet port; a main combustor chamber coupled tothe catalytic reactor; and an outlet port coupled to the main combustorchamber, the first source being configured to provide the primary fueldirectly into the main combustor chamber such that the primary fuel isatomized and vaporized within the main combustor chamber to produce aprimary fuel vapor, wherein when the combustion system operates at analtitude higher than a first predetermined altitude threshold, thecombustion system is configured to use the second source to provide thesecondary fuel into the inlet air port such that the secondary fuelmixes with air entering the inlet air port, and to cause the mixture ofthe air and the secondary fuel to combust in the catalytic reactor toproduce a gaseous secondary fuel product that flows into the maincombustor chamber, such that the main combustor chamber contains a firstproportional amount of the primary fuel vapor and a second proportionalamount of the gaseous secondary fuel product.
 2. The combustion systemof claim 1, wherein the first predetermined threshold altitude isgreater than or equal to 60,000 feet above sea level.
 3. The combustionsystem of claim 2, wherein as the altitude at which the combustionsystem increases from 60,000 feet above sea level to a secondpredetermined altitude threshold, the first proportional amountdecreases and the second proportional amount increases.
 4. Thecombustion system of claim 3, wherein the second predetermined altitudethreshold is greater than or equal to 95,000 feet above sea level. 5.The combustion system of claim 3, wherein when the combustion systemoperates at an altitude higher than the second predetermined altitudethreshold, the system is configured to operate by using the secondaryfuel exclusively at altitudes less than or equal to a thirdpredetermined altitude.
 6. The combustion system of claim 5, wherein thethird predetermined altitude is greater than or equal to 110,000 feetabove sea level.
 7. The combustion system of claim 1, wherein thesecondary fuel is produced by decomposition of a monopropellant.
 8. Thecombustion system of claim 7, the monopropellant comprising hydrazine.9. The combustion system of claim 1, wherein the secondary fuel isproduced by gasification of a pure fuel.
 10. The combustion system ofclaim 9, the pure fuel being selected from the group consisting ofhydrogen, methane, and propane.
 11. A combustion system for performingstable combustion and flame stabilization at high altitudes, comprising:a first source for providing a primary liquid hydrocarbon fuel; a secondsource for providing a secondary gaseous fuel; an inlet air port; acatalytic reactor coupled to the inlet port; a main combustor chambercoupled to the catalytic reactor; and an outlet port coupled to the maincombustor chamber, wherein when the combustion system operates at analtitude lower than a first predetermined altitude threshold, thecombustion system is configured to use the first source only to providethe primary fuel directly into the main combustor chamber such that theprimary fuel is atomized and vaporized within the main combustor chamberto produce a primary fuel vapor, and wherein when the combustion systemoperates at an altitude higher than the first predetermined altitudethreshold, the combustion system is configured to use the second sourceonly to provide the secondary fuel into the inlet air port such that thesecondary fuel mixes with air entering the inlet air port, and to causethe mixture of the air and the secondary fuel to combust in thecatalytic reactor to produce a gaseous secondary fuel product that flowsinto the main combustor chamber.
 12. A method for performing stablecombustion and flame stabilization at high altitudes, comprising thesteps of: providing a primary liquid hydrocarbon fuel to a maincombustor chamber; atomizing and vaporizing the primary fuel to producea primary fuel vapor within the main combustor chamber; when an altitudeat which the combustion is performed exceeds a first predeterminedthreshold altitude, providing a secondary gaseous fuel to an inlet airport such that the secondary fuel mixes with air in the inlet air port;and combusting the mixture of air and secondary fuel in a catalyticreactor to produce a gaseous secondary fuel product that flows into themain combustor chamber, such that the main combustor chamber contains afirst proportional amount of the primary fuel vapor and a secondproportional amount of the gaseous secondary fuel product.
 13. Themethod of claim 12, wherein the first predetermined threshold altitudeis greater than or equal to 60,000 feet above sea level.
 14. The methodof claim 13, wherein the step of combusting the mixture of air andsecondary fuel in a catalytic reactor further comprises the step ofcombusting the mixture of air and secondary fuel in a catalytic reactorto produce a gaseous secondary fuel product that flows into the maincombustor chamber, such that the main combustor chamber contains a firstproportional amount of the primary fuel vapor and a second proportionalamount of the gaseous secondary fuel product and such that as thealtitude at which the combustion system increases from 60,000 feet abovesea level to a second predetermined altitude threshold, the firstproportional amount decreases and the second proportional amountincreases.
 15. The method of claim 14, wherein the second predeterminedaltitude threshold is greater than or equal to 95,000 feet above sealevel.
 16. The method of claim 14, wherein when the combustion systemoperates at an altitude higher than the second predetermined altitudethreshold, the method further comprises the step of using the secondaryfuel exclusively at altitudes less than or equal to a thirdpredetermined altitude.
 17. The method of claim 16, wherein the thirdpredetermined altitude is greater than or equal to 110,000 feet abovesea level.
 18. The method of claim 12, wherein the secondary fuel isproduced by decomposition of a monopropellant.
 19. The method of claim18, the monopropellant comprising hydrazine.
 20. The method of claim 12,wherein the secondary fuel is produced by gasification of a pure fuelselected from the group consisting of hydrogen, methane, and propane.